Solvent treatment



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SOLVENT TREATMENT Harland H. Young, Western Springs, Howard G. Black, Chicago, 111., assignors to Swift 8; Company, Chicago, Ill., neor oration of Illinois N Drawing. Application April -7, .1951, Serial 0- 219,894, now Patent No. 2,682,550, dated hmegl fi, 1954, which is-a divisipnv of application S ep' al N9. 567,126, December 7, 1944, now Patent No. 2,553,288,

dated May 15, 1,951. Divided andthis application mine 11, 1951, Serial No. 231,043 g p 22 Claims (Cl. zoo-#41039 This invention relates to the "fractionation of fatty "esters and has to do more particularly with the separationof glycerides of higher fatty acids into fractionsof varying degrees of saturation and meltingIpo i-nt by solvent treatment. The invent-ion involves the purification and fracdonation of various esters of polyhydric alcohols; for example, .glyceride oils including triglycerides and partial glycerides, such as monoand diglycerides. The invention hasp'articular application to the treatment of both animal and vegetable fats; for example, the des'tearinating or animal fats such as white and yellow grease to produce stearine and grease oil, the purification and separation of monoand diglycerides from mixtures of mono-., di-.,

and triglycerides, and the separation of glycerid'es from the "fatty esters of higher monohydric alcohols such as occur in sperm oil.

Naturally occurring glycerides are made up of com- I ponents of varying degrees of saturation andmeltingpoint. In order to have maximum utility it is at times desirable to separate fractions of like degrees of saturation and melting point from the original mixture. The common method used in the past for accomplishing "this .separation has been the "so-called seedin in ,Whic hthe melted fatty material is slowly chilled. The more saturated porti'ons crystallize and are separated by a straining orlpressing operation. Solvent fractionation has been proposed as, a means for separating the more saturated fror'rithe less saturated fractions, but experience has shown that as sharp a separation as desired is notobtained. A sharp separation can be obtained if the fatty material is dissolved in a solvent and chilled until the higher melting point constituents crystallize. The solid material is then filtered on and washed with fresh chilled solvent.

By dissolving the fatty material in a solvent, generally at an elevated temperature, and cooling the mixture gradually, a fraction precipitates which consists of the higher,

melting, more saturated constituents. If "the cooling and separation are carried out properly the fraction which separates is quite uniform in degree of saturation and melting point and consists of products of quite similar chemical constitution and physical properties. After the solid precipitate has been "removed, further. cooling of the filtrate results in the separation of a further fraction which is somewhat less saturated and of slightly lower melting poin't'than the original precipitate. The filtration and cooling'ste 's may be continued to yield any number of fractions, each with different melting point and degree of saturation. If the process is carried out carefully, quite sharp separation can generally be obtained. "It further degree 'of separation is desired, any of the fractions can be redissolved in a portion of the solvent or another solvent and re'chille'd and filtered in a manner similar to the original chilling and filtering. By repetition of this procc'ss fractions of high degree of uniformity and purity can be produced.

.Fatty acid glycerides, particularly fatty acid mono- 2,740,799 Firestone 3: 56

purposes because of their surface activity, compatibility with numerous materials and other desirable physical and chemical properties. In recent years many methods have been described for the preparation and use of these fatty acid glycerides. in general, however, these procedures do not produce simple mixtures of monoglycerides, but instead they usually form compositions containing in addilion to the monoglycerides some diglycerides and triglycerides, as well as other organic and inorganic impurities. Among the methods disclosed in prior patents is that-of Kapp, U. S. Patent No. 2,207,257, wherein a mixture of fatty acid mono-, di-, and triglycerides ex tracted from soaps of the corresponding fatty acids. The resulting product is, as stated hereinbefore, a mixture of materialsysome of which are not desired.

Another object of'this invention is to separate mixtures of fatty 'acid ;glyce'rides into uniform fractions, each possessing diiferent physical and chemical properties.

Another object of the invention is to provide an improved process for separating glyceride esters and esters of *Oihfil'fPOlYhYdllC alcohols by fractional crystallization.

Another object of this invention is to produce relatively pure --fractions of fatty acid partial esters having uniform un'saturatio'n, solubility, stability, surface activity and other desirable properties.

:An additional object --is to provide an economical process for solvenbext'racting fatty acid monoglyce-rides --in order 'to purifysaid materials.

A further object of the invention is to provide improved solvents for separating fatty acid .rglycerides by solvent crystallization.

further object of the invention is to produce relatively pure fractions of fatty acid partial glycerides having uniform unsaturation, solubility, stability, surface activity, and other desirable properties.

A-n additional object is to provide an economical proctionsof esters, and separating the fractions so separated.

One method is to form a solution 'ofa mixture of esters in a crystallization solvent-having a -di-lferential solubility for the various components of the mixture, utilizingsufiiciently high temperatures to completely dissolve-the oil,

chilling the solution to separate the desired fractionas glycerid'e's, are employed in manyways and for different I crystals, and then separating the crystals from the remaining solution by suitable means such as filtration or gravity separation. Generally, when a solution of the fatty material and a solvent is chilled or when an antisolvent is added, the material which first precipitates is the higher melting, more saturated fraction. 7 As the temperature is further reduced, the less saturated, lower melting point fractions begin to precipitate. By controlling theamount of solvent and the temperature, any desired number of fractions maybe separated.

The present invention maybe used for separating various types of .glyceride fats including triglyceride, 'digl'ye'eride, fmonoglyceride or mixtures thereof.

broad principles of the present invention may be applied to any of the aforementioned materials, although the specific details of the invention may have to be varied depending on the species of the material treated. In pr'aoticing the invention it isdesirable to use conditions most favorable to the vparticular solvent being employed.

Thus the temperature and the solvent ratio may have terial dissolved is usually lower; hence, it is a question of balancing the degree of separation against the quan' tity of solvent required. In general, it is necessary to use only sufficient temperatures to obtain solution of the oil in the solvent. Usually these temperatures will be within the range of about room temperature (about 70" F.) to about 200 F. The proportion of solvent to ester material under treatment will usually be within a range of about 1 part to 15 parts by volume of solvent to 1 part of oil. For simple single-stage crystallizations a proportion of about /2 to 5 parts of solvent to 1 part of ester material is satisfactory, and preferably about 1-3.

One aspect of the present invention comprises the purification and/or fractionation of partial esters of aliphatic polyhydroxy substances occurring in mixtures containing these materials by solvent extraction with a selective solvent. It has been found that when a polar solvent is contacted with mixtures containing partial esters of aliphatic polyhydroxy substances, there is a greater tendency to dissolve the polyhydroxy substances having the lower number of ester substitutions than those more fully esterified, and the more unsaturated derivatives than the more saturated ones. By this means the applicants can extract concentrated monoglycerides from mixtures containing diand triglycerides, and/or to separate monoglycerides into unsaturated and saturated fractions. portions and under such conditions that two phases are formed; one, a solution of the aliphatic polyhydroxy substances having a larger number of free hydroxyl groups; and the other, an insoluble or at least partially immiscible phase containing some impurities and more fully esterified polyhydroxy compounds. One method is to operate so that two liquid phases are formed; in other words, to employ liquid-liquid extraction.

When employing liquid-liquid extraction it is within the scope of this invention to employ continuous counter-current extraction (in a tower), multiple-stage counter-current extraction (mixing and settling), or one or more stages of batch extraction (mixing and settling). In any of these procedures one or more miscible polar solvents may be used to effect controlled and/or maximum fractionation. In addition, it may be advantageous to use one or more immiscible non-polar solvents in conjunction with the polar solvent or solvents in order to set up an opposed solubilizing action on the more fully esterified polyhydroxy substances when using polar materials possessing very high solvent action or when operating on mixtures of partial esters which have many solubilizing groups, such as olefine linkages or hydroxy radicals. It is also a feature of this invention to employ miscible non-polar solvents or miscible anti-solvents along with the polar solvents in order to improve or reduce, i. e., control, the solvent properties on the materials which are not desired to be extracted. For example, water-saturated solvents are in many cases more selective than the corresponding anhydrous materials. In other cases a highly effective but non-selective miscible solvent may be added to a very selective solvent to increase the yield.

In operating this process it is possible to employ temperatures and proportions which yield immiscible liquids at all times. This is the case in the preferred method of operating in a continuous counter-current manner. The procedure in this type of operation usually is to flow the mixture containing partial esters of polyhydric alcohols, with or without non-polar solvents, such as petroleum ether, into a vertical tower near the bottom or at any point substantially below the top thereof. Simultaneously, a polar solvent, such as furfural, is introduced into the tower near the top. If desired, the tower may be equipped with packing, bafiles, plates and/or heating units to vary or control the temperature throughout the extraction. The denser solvent flows downward- The polar solvent is employed in such pro- -ly through the column counter-current to the rising mixture of aliphatic polyhydroxy derivatives. An interface will be formed at one point in the tower between the lower downwardly flowing solvent phase through which the partial esters rise in the form of drops or the like, and the upper rising extracted partial ester phase through which falls the fresh solvent. This interface is usually midway between the two inlet ports but may be nearer to either of them, depending on the characteristics of the material under treatment and the extractant. It is also desirable to have a separating zone below the lower and above the upper entrance ports for the materials to be counter-currently treated in order to permit complete separation of the immiscible phases. For effecting maximum concentration it is another feature of this invention to separate the solvent from the extract and to return a portion of the extracted material to the tower at a point near the bottom but below the entrance port of the original mixture undergoing extraction. By this process of reflux it is possible to even further concentrate and purify the less highly substituted polyhydroxy partial ester. With solvents, such as alcohol, having a lower density than the oil, the oil is introduced near the top and the solvent near the bottom.

The above outlined procedure can be also conducted in a counter-current, multi-stage manner including the reflux feature. In such operation the solvent is flowed into the last of a series of batch treating stages and the mixture to be purified is introduced into the first, or into an intermediate stage if reflux is to be employed. The raffinate from each stage moves progressively toward the last stage and the extract from each stage moves progressively toward the first stage. When employing reflux, the extract from the first stage is separated from its solvent and a substantial portion of the purified solventfree extract of less fully esterified material is returned as the charge to the first stage. In each of these stages the raffinate. from the previous stage and the extract from the following stage are intimately mixed for a substantial period. The mixture is then permitted to settle and the two layers are separately drawn off, one representing' the raflinate charge to the following stage, and the other representing extract charge to the next previous stage. The rafiinate from the last stage comprises the more fully esterified and more saturated polyhydroxy dcrivatives.

Another procedure involves concurrent extraction by flowing the material to be extracted in a mixture with the polar solvent through a zone wherein the conditions are such that the materials are miscible; for example, higher temperatures and/or higher proportions of solvents. The materials are held in this condition for a suflicient time to effect uniformity of solution; for example, by flowing through a pipe of relatively small cross-section and tortuous path. After complete mixing, the mixture is treated so that incipient stratification (turbidity) takes place; for example, by cooling the mixture, by evaporation, or by addition of an immiscible, non-polar solvent (e. g., hydrocarbon) or a miscible non-solvent (e. g., water). The material in this turbid state is subjected to centrifugal action in order to effect separation of the suspended matter, i. e., the material causing turbidity. This process may involve the simultaneous stratification and separation during the centrifugal treatment. It is also possible to cool or precipitate by other means to an extent that immiscible layers are formed, but the preferred procedure involves the centrifugal action because of the more rapid separation effected.

Of course, simple batch extracting in a single or a plurality of stages, each employing fresh solvent, can be used, but this is not generally employed in commercial operation because of the higher cost and poorer yields involved.

The process, as stated hereinbefore, is directed to the liquid-liquid extraction of the partial ester mixture. Such procedures may .also'include operations wherein a solid phase is formed in addition to the two liquid phases. in-v other words, a double purification :is elfectedby separation of the three phases.

The processes involving solid-liquid extraction may be,

conducted in the following manner, amongother methods: 1

A .solid, plastic composition of partial esters may -be admixed with a polar solvent at a temperature .below that at which thevcomposition becomes liquid. .After the composition has been intimately mixed with the solvent,

the insoluble extracted portionis separated by means of centrifuging, filteringand/or decanting. .The liquid'extract is treated to remove the solvent which may be re- .turnedfor extracting additional composition under treatment. The material removed from the solvent is a fraction of po'lyhydroxy material of lower degree of substitution. The process may be repeatedlin one or more stages employing the same or different solvents or mixtures of solvents.

Other methods include the complete dissolution of the mixture in the polar solvent or solvents with or without misciblepompolar solvents and non-solvents at higher temperatures followed by the vfractional precipitation or crystallization of the polyhydroxy material having a higher degree of substitution from the solution by lowering the temperature and/or by addition of a miscible nonsolvent. The separated material may be removed by cencontaining the partial esters by means of polar solvents.

The addition of a water-immiscible polar solven't or solvent combination will cause aqueous material to separate to a major extent from the resulting solution of partial esters of polyhydric alcohols. This separation may be effected under conditions that totahmiscibility of the solvent and ester composition results or under conditions that fractionation takes place. Non -polar solvents in conjunction with the polar solvents are also effective .for this purpose. When employing polar solvents, miscible wholly or partially with water, it is possible to cause water separation by the addition of salts of inorganic acids or of low molecular weight organic acids such as sodiurnchloride, sodium sulphate, sodium phosphate, sodium carbonate, sodiun 'borate, sodium acetate or the corresponding ammonium or other alkali metal. r

salts. An immiscible aqueous salt solution or salt layer will separate out, and if any inorganic salts and other water-soluble impurities are present these will probably 'be removed too. Hence the process is not only one of fractionation, but also involves simultaneous purification and extraction from other materials. I

The's'ource of the partial esters is immaterial and they may 'be prepared by any of the methods described in the numerous patents and literature articles. Because of the various sources many different types of admixed agents and impurities are separated by the present process. Among the methods for preparing the materials which may be purified by the method of the present invention are those described in Christensen, U. "S. Patent No. 2,022,494; Edeler et'aL, U. S. Patents No. 2,206,167 and No. 2,206,168; Kapp, U. S. Patent No. 2,207,251; Oelverwertung, Austrian Patent No. 67,061; and Jurgens, German Patent No. 277,641. 'This list is merely "by way of illustration and the present process is not limited. to

The extraction solvents 'which may be employed in the present invention are non-reactive polar solvents, preferably organic. Among these solvents are the lretones.

, We have found short chain aliphatioketones, particularly those ketones having from 3 to '6 carbon atoms ,per molecule to be efiective .as the solvent. It is essential that the properties of these materials, that is, the leetone solvent, and the temperatures employed should be such that two .phases are formed and that the solvents are not reactive under the treatment conditions. Miscible polar solvents which do not meet the above requirement and also miscible nonpolar solvents may be used inconjunction with the selective polar solvents to be employed in they present process in order to alter the solubility of certain of the constituents under treatment. Likewise,.it

.ispossible to increase the selectivity of the process by employing non-miscible nonpolar solvents which tend to hold the more fully esterified materials while the polar solvent extracts the less vesteritied more hydrophilic material. 1

Among the polar solvents which may be employed for thepresent purposes are acetone, diacetyl, diacetone alcohol, acetonyl acetone, and acetone plus sulphur dioxide.

The temperature of operation as indicated hereinbefore will depend mainly on the method of treatment, the type of solvent, the proportion of solvent, and the material under treatment. In general, the solvents are more selective at lower temperatures but the quantity of material dissolved is usually lower; hence it is a question of balancing the degree of separation against the quantity of solvent necessary. When liquid-liquid extraction .is the desired method, of course a low temperature limit is set by the temperature of solidification of one or both of the phases. A high temperature limit is similarly fixed in most cases by the fact that the polar solvents will either become completely miscible with the total ester mixture under treatment or will dissolve. abnormally large quantities of all constituents in the ester mixture.

The proportion of solvent to ester material under treatdistillation, and precipitation by the addition of nonsolvents such as water. For large scale production it is desirable to recover the solvents for return to the process in "the treatment of fresh materials. V

The fractional crystallizationor precipitation of the partial esters from the extract solution has the additional merit of removing substances which in many cases have a deleterious action in the extracted product. In some cases these materials will precipitate first from the solvent solution, but in general it has beenfound that they are among the last materials to be precipitated or crystallized from the extracting solvent. Hence by the processes of this invention it is possible not only to fractionate and purify the partial esters, but also to effect an improvement in color, taste and odor, and the stability of the product in resistance to reversion in these proper'ties.

The fractionation and purification process may be performed in a single unit with a single solvent, but in many cases there are advantages in operating in several extracting steps of the same type or different types with the same or different solvent or solvents; for example, one

solvent may be eifective for concentrating the esters of aliphatic polyhydroxy substances of lower degree of 'sub- 'stitution when these materials are present in small percentages, but the same solvent may be much less selective when the concentration of the constituent to be extracted is present in higher proportions. On the other hand, another solvent may have a directly opposite change of selectivity; that is, be more effective in concentrated mixtures than on dilute mixtures. Hence, when starting with a material having a low content of slightly esterified materials, the first stage of extraction would be with the former solvent, and the extract of the solvent from the first stage of extraction could then be extracted in a second stage with the latter solvent. In another case, the first stage of extraction may be one involving simple or concurrent mixing and settling to remove a small or large proportion of the constituents of the material under treatment followed by a counter-current extraction of the solvent-free extract and/or of the raffinate from this first stage of extraction. As another variation, it is possible to obtain an extract of a mixture containing esters of aliphatic polyhydroxy substances in a polar solvent and then to extract this solution by any method, preferably continuous counter-current extraction with an immiscible solvent, such as gasoline, petroleum ether or other nonpolar solvents. Any combination of solvents or mixtures of solvents and/or of methods disclosed herein may be employed in the present process. By nonreactive solvents it is meant to include solvents which do not react with the hydroxy substituted derivatives under the conditions of treatment.

The fractions obtained by these extraction procedures,

with or without the solvents present, may be treated with adsorbent agents, such as activated carbon, bauxite, kieselguhr, silica gel and clay, alkali or other purifying agents to yield final products of unusually high purity. Although the above description has been directed to the treatment of partial esters of polyhydroxy compounds, it is likewise applicable to the fractionation and purification of organic acid amides of aminoalcohols, such as monoethanolamine, diethanolamine, trishydroxy methyl aminomethane, monoglycerolamine, diglycerolamine, and the like. That is, the process is applicable to the esters or amides having free hydroxy groups. The products of the present process may be used wherever the corresponding nonpurified full and partial esters and/ or amides have previously been employed. 'l" he agents having free hydroxy groups are exceptionally satisfactory for use as emulsifying agents for emulsifying or for other surface-active purposes. The agents are unusually effective in food preparation, such as ice cream, shortening, peanut butter, and the like, because of their greater efficiency, their purity and their greater resistance to reversion. The full esters are likewise improved in color, odor, taste and stability and may be used in foods, lubricants, soap manufacture, manufacture of partial esters, and organic synthesis. l'he partial esters by themselves possess surface active properties, but for particular purposes these purified compounds may be reacted with inorganic polybasic acids to form the corresponding partial esters thereof, which, when neutralized, are highly desirable surfaceaetive agents possessing deterging, emulsifying, penetrating and wetting properties.

Another aspect of the invention involves the separation of esters of polyhydric alcohols by solvent crystallization. According to this method the product to be treated is dissolved in the solvent at an elevated temperature and the mixture cooled to precipitate or crystallize fractions of: varying degree of saturation and melting point. The fractions crystallized may then be separated from the solvent by suitable means such as filtration. By reducing the temperature in carefully controlled intervals a plurality of fractions of similar chemical and physical properties may be produced. The crystallization method is particularly applicable to the treatment of full esters such as triglycerides, but it may be applied to the separation of partial esters or mixtures of full and partial esters by properly selecting the solvent or mixtures of solvents. When products eontainin two or more compounds of the group of monoglycerides, diglycerides and triglycerides are treated, the order of crystallization from polar solvents is usually triglycerides, then diglycerides and then monoglycerides. Thus in the treatment of mixtures of triglycerides, diglycerides and monoglycerides with a solvent such as ethyl alcohol aud chloroform, the mixture may be separated on reducing the temperature by crystallization in the reverse order of the number of free hydroxyl groups. In general, the same order applies also to other partial esters. When treating a product comprising essentially full esters distinguished from partial esters, for example, triglycerides as distinguished from monoglycerides and diglycerides, the order of crystallization is usually according to the degree of saturation and melting point, i. e., the more saturated and higher melting point components crystallize first.

The crystallization method differs from the liquidliquid phase operation in that the separation according to the degree of unsaturation is not so pronounced in the crystallization method. On the other hand the crystallization method gives sharper separation according to the melting point and completeness of saturation and length of carbon chain, whereas the liquid-liquid phase extraction tends to make a separation between the unsaturated and saturated fractions. It is not possible by such method to obtain a sharp separation between products of the same length of carbon chain.

In the solvent liquid-liquid extraction operation the separation is made on differences in degree of polarity of the compounds to be separated. \lithin the class of fatty materials the degree of polarity varies only over a rather narrow range, and it is, therefore, ditficult to make a sharp separation. On the other hand, in the solvent crystallization process the separation is made on the basis of the difference in melting point and solubility of the various fatty materials. The melting point varies over quite a wide range, and it is therefore possible to make quite sharp separations if the proper conditions are chosen.

The melting point of the fatty material effects the degree of solubility to a greater extent than does the degree a of unsaturation. It is, therefore, possible to make a more limited number of cuts can be made.

marked separation on the basis of melting point than on the basis of unsaturation.

To illustrate, attempts have been made to separate fatty materials on the basis of unsaturation by means of solvent crystallization. However, the degree of solubility be tween the saturated and unsaturated constituents is not sufiiciently different to make sharp separations and only a On the other hand when the separation is made on the basis of melting point where large differences exist in the degree of solubility, a large number of cuts can be made. each possessing widely different melting points. 7

In the solvent crystallization process the degree of separation on the basis of melting point can be controlled to some extent by the method in which the process is carired out. If the crystallization is carried out rapidly, causing a quick crystallization of the higher melting point constituents, some of the lower melting constituents are likely to be adsorbed or occluded on the crystals, thereby causing a lesser degree of final separation. However, if the crystallization is carried out slowly, and if the solvent ratio and temperature are adjusted, the adsorption and occlusion are held at a minimum. Further, if the crystals are well formed and granular they can be washed with cold solvent, washing away from them the lower melting point constituents which are adsorbed, resulting in a separation which is considerably sharper.

In the solvent extraction process such control is not possible. Further, the crystallization process when applied in a manner to obtain separation on the basis of melting point as contrasted to that intended to cause separation on the basis of unsaturation is more easily controlled in that the crystals are more readily formed and less occlusion takes place, resulting in a sharper separation.

Examples of the ketones are acetone, methyl ethyl ketone, methyl butyl ketone, diethyl ketone, ethyl propyl dismay-1 i n m rnlbu rlv setu s, :dib tv k t n stvl. -diacetne alcoh ia ctonyl aceton It may be desirable in some cases to usennizttures of .two or more of theabovesolvents.

Instead of chilling the mixture of solvent and ester of polyhydric alcohol .in ,ordento cause crystallization, an antisolvent may be added. 'Ihe antisolvent a material may be polar, low molecular weight compounds. Zlhe .most common are water and the lower aliphatic alcohols such ,as methyl and ethyl alcohol. The temperature at which they are used will vary, .dependi11g upon the fat solvent whichisrused,,andthe-type of fatty material which is in solution. At times it is advantageous {to use a com- -.hination :of cooling and the'zantisolvent. It is ,generally filter which the solid material is removed as a filter cake on .a segmented rotating drum. The filter cake may 'bewashed .by a portion of the coldsolvent and the used wash solvent be reused in the system; .for example, bymixi g it with the charge to the filter. The solvent may be stripped from the filter cake and the filtrate in sui able s rippersfiene ial y, -.th e softer.the fiatty material .used, the smaller the amount .of the solvent required to cause complete solutio :at elevated temperatures. .As the melting point of the original .fatty material increases, more solvent is necessary in orderto obtainlcornpleteisolation. Generally, for the common fatty materials, such inedible greases and soybean oil from one-half to five volumes and preierab lyone to three volumesofsolvent toone volume of .oil suffices. However, with the more saturated higher melting point ,fattymaterials such as fallow and substantially complete y hydrogenated texts .or oils considerably more .solvent'may be necessary, for example up to :ten volumes-of solvent to one of .fat.

The temperature of .solution also depends on the solvent used and the melting point of the fatty material. For example, normal propyl alcohol dissolves an equal volume oflard at 100 F. "Normalbuty-l alcohol dissolves an [equal volume of lard at 80 F. while normal amyl.

alcohol dissolves lard at room temperature. .the

chain length of the alcohol increases, solution is obtained at" slower temperature. Generally, temperatures .from

room tfimpfirature (about 70 .F.) to .1 00" F. are satisfactory. l-lowever,ternperatures up to the boilingppint of the alcohol may he necessary in order .to obtain iQQln' plate, solution with the higher melting ,fats such as tallow and hardened fats or oils. The fatty materials'erystallize from the alcohol at temperatures varying with the alcohol used and the type of fatty material dissolved. The higher the melting point of the fatty material used, the higher will be the temperature at which crystallization begins. .Overall temperatures within the range of 100 F. .down to 10 P. will generally be satisfactory.

When using an auxiliary solvent in separation of mono-, .diand triglycerides the temperature at which the triglycerides separate is below their melting point, and therefore they-crystallize in well-formed crystals. However, if the auxiliary solvent .is not employed, separation f th t iglycerid material its-a a temper ture which is generally above the melting point of the triglyceride :mater al, aud therefor r mains as n u ;t o n of oils g ne al y gi e a ss h rp d gree o separation than when crystals separate. Nevertheless, the separation of the triglyceride material as an oil when the auxiliary solvent is not employed is quite pure, and if the in which fats are insoluble .oronly slightly soluble. They :10 proper-means are ava lable for separating the oilfrom .fth es sut eir yrs qdssp i n dbwinsd- The separation of crystals ,is mucheasier to accomplish on a practical scale than is .the separation of .oily mate- ..rials. IEhe erystals can ,be washed with pure solvent,

resultingjn asharper degree-of separation,v

' 1f the ratio of solvent .tothe mixture .of mono, :di- .and

ing from 3 to .6 carbon atoms are vbest adapted for crys- .tallization. The .fatty materials generally crystallize in granular crystalsirom this class .of solvents. The amount of solvent required varies, depending .upon thermolecular weight and melting .point .of the fatty material. Generally',.one-,halfto live volumes of solvent for-one volume of fatty material is required. However, there maybe cases where .up to ten volumes ofrtheketonemay be necessary. The temperature .reguiredfor solution .is generally. quite low, approximating the range from room temperature to 100" IF. However, in the ,case of the lower molecular weight ltetones and the higher melting tpomt fatty material, considerahlylhigher temperatures up .to the boiling point of the .ketone may .be required in order to obtain complete solution. Factor es-can be used to dissolve both completely esteriiied and partial esters of polyhydric alcohols .and are suitable for crystallization of either types nttatty materials.

Example 1 A sample ifif white grease dissolved in an equal volume of acetone at sroomttemperaturezandchilled under :agitationto about 40 ifihe mixture was then filtered ZlhlfOlIgh ta vacuum .iilter, using :a canvas :covering as the 'filteringsunface. :Adter filtration was completed -.the'p1:e

.acipitategcontainirrg essentially the .glycerrdes :of :stearic :and palmiticaacidswas washed ;on :the filter with a-small quantity .of acetone at about 40 F. The solvent was removed from both the filtrate and the precipitate by vacuum distillation. The fraction whichzprecipitated consisted of "about .20 :per cent :of the original weight of the grease :and had a melting tPOlIlI rot about 'C. and .au

. iodine znurnber of about The filtratehad a melting point-of about 30* LC- and an iodine anumher'of about v Example TI Refined .and bleached cottonseed :oil were dissolved .in :313} equal volume of, methyl ethyl ketone at 100 F. and chilled under agitation to about 40 F. s The mixture was filtered by means of a vacuum and the precipitate washed with a small quantity of chi ed solvent. 'The solvent was removed lh'omboth the filtrate and precipitate by vacuum distillation. The precipitate containing the glycerides o'f therrrore saturated'fatty acids consisted of about 20-per cent of the original oil and had an iodine number of 102 and a melting point of and the filtrate had an iodine number of 112 and a cold test of about 30 hours and amelting-point of 30 It will be observed that the separation was made on the basis of melting point in preference to separation on thebasis of unsaturation.

gExample III 'Refined and bleached cottonseed 'oil were dissolved in "an equal volume of methyl butyl ketone at room temperatdacottonseed-oll was washed on the filter with a small quantity of methyl butyl ketone at about 30 F. The solvent was removed from the precipitate and filtrate. The oil in the filtrate consisted of about 72 per cent of the original oil and had an iodine number of 111, a pour point of 10 F. and a cold test of 19 hours. The stearin or precipitate fraction had a titer of 42.2 and an iodine number of 89. The latter consisted of about 28 per cent of the original oil.

The ester material may be recovered from the solvent solution by crystallization, vacuum distillation, flash distillation, or precipitation by the addition of non-solvents such as water. For large scale production it is desirable to recover the solvents for return to the process in the treatment of fresh materials.

The fractional crystallization or precipitation of the esters from the solution may be used to remove substances which in many cases have a deleterious action in the product. In some cases these materials may be precipitated first from the solvent solution, or they may be among the last materials to be precipitated or crystallized from the heating solvent. Hence, by the processes of this invention it is possible not only to fractionate and purify the esters, but also to effect an improvement in color, taste and odor, and the stability of the product in resistance to reversion in these properties.

The color, flavor, stability and reversion causing materials in fats is due to the presence of compounds of quite different chemical nature from the fats themselves. Their solubilities are also difierent, and by the use of the proper solvent and temperature it is possible to separate them from the fatty materials. For example, the compounds in soybean oil which cause reversion may be separated from the oil by converting the hydrogenated oil to monoglycerides and crystallizing the monoglycerides from ethyl alcohol. The monoglycerides are precipitated and the reversion causing materials remain in solution. The color of animal fatty materials, such as tallows and greases, is due to the presence of pigments and decomposition products of the fats and their animal tissues. These foreign materials and decomposition products may be separated from the fatty materials by crystallization of the fats from suitable solvents. The foreign material and decomposition products have different solubilities than the fats and, therefore, may be separated under proper conditions.

In the cases Where the color-forming bodies are less soluble than the fats, they precipitate at a higher temperature than the fats. However, in most cases the color-forming bodies are more soluble than the fats and remain in solution after the fats have been precipitated.

An example of the latter is the separation of the colors of soybean oil by crystallization from acetone. If soybean oil is dissolved in acetone and repeatedly crystallized, a Water-white oil is finally obtained and the color remains in the solvent.

The fractions obtained by crystallization with or without the solvents present may be treated with adsorbent agents such as activated carbon, bauxite, kieselguhr, silica gel, and clay, alkali or other purifying agents to yield final products of unusually high purity.

Obviously, many modifications and variations of the invention hereinbefore set forth may be made without distinguishing from the spirit and scope thereof, and

therefore only such limitations should be imposed as are 12 is also a continuation-in-part of application Serial No. 448,002, filed June 22, 1942, now abandoned.

We claim:

1. The method of purifyingmonoglycerides formed by superglycerinated refined fats to separate therefrom materials tending to cause reversion of flavor and odor, which comprises treating the monoglycerides with a short chain aliphatic ketone as the solvent therefor at a temperature at which a single phase is formed, reducing the temperature to cause the formation of two distinct phases, one of said phases containing monoglycerides and the other of said phases containing the reversion-causing material, and recovering the monoglycerides from the firstmentioned phase.

2. The method of purifying monoglycerides formed by superglycerinated refined fats to separate therefrom materials tending to cause reversion of flavor and odor, which comprises treating the monoglycerides with an aliphatic ketone containing from 3 to 6 carbon atoms per molecule as the solvent therefor at a temperature at which a single phase is formed, reducing the temperature to cause the formation of two distinct phases, one of said phases containing monoglycerides and the other of said phases containing the reversion-causing material, and recovering the monoglycerides from the first-mentioned phase.

3. The method of purifying monoglycerides formed by superglycerinated refined fatty acid triglycerides to separate therefrom impurities tending to cause reversion of flavor and odor which comprises treating the monoglycerides with a short chain aliphatic ketone as the solvent at a temperature at which the monoglycerides have said impurities dissolved in the ketone, cooling the solution to precipitate the monoglycerides therefrom, and separating said precipitate from the solution of impurities tending to cause reversion of flavor and odor.

4. The method of purifying monoglycerides formed by superglycerinated refined fatty acid triglycerides to separate therefrom impurities tending to cause reversion of flavor and odor which comprises treating the monoglycerides with an aliphatic ketone containing from 3 to 6 carbon atoms per molecule as the solvent at a temperature at which the monoglycerides have said impurities dis solved in the ketone, cooling the solution to precipitate the monoglycerides therefrom, and separating said precipitate from the solution of impurities tending to cause reversion of flavor and odor.

5. The method of purifying monoglycerides formed by superglycerinated refined vegetable fats to remove materials tending to cause flavor and odor reversion, which comprises treating the unpurified monoglycerides with a short chain aliphatic ketone as the solvent to dissolve the monoglycerides and reversion-causing material completely in said ketone, cooling the resulting solution to crystallize the monoglycerides relatively free from reversion-causing materials, and separating the crystallized monoglycerides from the solution containing the reversion-causing materials.

6. The method of purifying monoglycerides formed by superglycerinated refined vegetable fats to remove materials tending to cause flavor and odor reversion, which comprises treating the unpurified monoglycerides with an aliphatic ketone containing from 3 to 6 carbon atoms per molecule as the solvent to dissolve the monoglycerides and reversion-causing material completely in said ketone, cooling the resulting solution to crystallize the monoglycerides relatively free from reversion-causing materials, and separating the crystallized monoglycerides from the solution containing the reversion-causing materials.

7. The method of purifying partial glycerides formed by superglycerinated refined fats to separate therefrom materials tending to cause reversion of flavor and odor, which comprises treating the superglycerinated refined fat containing substantial amounts of partial glycerides with a short chain aliphatic ketone as the solvent to dissolve completely the partial glycerides and reversion-caus- 13 ing materials, cooling the resulting solution to precipitate the partial glycerides, and separating the said partial glyceride precipitate from the solution of reversion-causing material.

8. The method of purifying partial glycerides formed by superglycerinated refined fats to separate therefrom materials tending to cause reversion of flavor and odor, which comprises treating the superglycerinated refined fat containing substantial amounts of partial glycerides with an aliphatic ketone containing from 3 to 6 carbon atoms per molecule as the solvent to dissolve completely the partial glycerides and reversion-causing materals, cooling the resulting solution to precipitate the partial glycerides, and separating the said partial glyceride precipitate from the solution of reversion-causing material.

9. A process snbstantnally as described in claim 8 wherein the ketone solvent is dipropyl ketone.

10. A process substantially as described in claim 8 wherein the ketone solvent is diethyl ketone.

11. A process substantially as described in claim 8 wherein the ketone solvent is methyl butyl ketone.

12. A process substantially as described in claim 8 wherein the ketone solvent is methyl ethyl ketone.

13. A process substantially as described in claim 8 wherein the ketone solvent is acetone.

14. A process for the manufacture of partial glyceride esters of a fatty acid which are free of flavor and odor, comprising subjecting a refined glyceride fat which has been hydrogenated and treated with glycerine to convert said fat into a mixture containing a substantial propor tion of partial glycerides to solvent treatment with a short chain aliphatic ketone at a temperature such that a single phase is formed, reducing the temperature so that two distinct phases are formed, one of said phases comprising a solution of said ketone and the material tending to cause reversion of flavor and odor, and the other phase comprising the partial glycerides, separating the phases and recovering the partial glycerides free of reversion causing material.

15. A process for the manufacture of monoglyceride esters of a fatty acid which are free of flavor and odor, comprising subjecting a refined glyceride fat which has been hydrogenated and treated with glycerine to convert said fat into a mixture containing a substantial proportion of monoglycerides to solvent treatment with a short chain aliphatic ketone as the solvent at a temperature such that a single phase is formed, reducing the temperature so that two distinct phases are formed, one of said phases comprising a solution of the ketone solvent and the material tending to cause reversion of flavor and odor and the other phase comprising the monoglycerides free of reversion causing material, separating the phases and recovering the monoglycerides free of reversion causing material.

16. A process substantially as described in claim 15 wherein the ketone solvent is dipropyl ketone.

17. A process substantially as described in claim wherein the ketone solvent is diethyl ketone.

18. A process substantially as described in claim wherein the ketone solvent is methyl butyl ketone.

19. A process substantially as described in claim wherein the ketone solvent is methyl ethyl ketone.

20. A process substantially as described in claim wherein the ketone solvent is acetone.

21. A process for the separation of fatty acid glycerides into fractions having substantially uniform chemical and physical properties, which comprises admixing the fatty acid glycerides with a short chain aliphatic ketone at a temperature correlated with the amount of the ketone to cause the formation of a distinct phase comprised predominantly of higher fatty acid esters dissolved in the ketone solvent and having substantially uniform chemical and physical properties, and recovering said esters free of the rietone solvent and esters having substantially dilferent chemical and physical properties.

22. A process for the separation of fatty acid glycerides into fractions having substantially uniform chemical and physical properties, which comprises forming a solution of the fatty acid glycerides with a short chain aliphatic ketone as a solvent, cooling the said solution under controlled conditions of temperature and volume of solvent to crystallize a fraction containing fatty materials of similar melting point, and separating said crystallized fraction from the said solvent and fatty materials having substantially difierent chemical and physical properties.

References Cited in the file of this patent UNITED STATES PATENTS 2,459,820 James Ian. 25, 1949 

1. THE METHOD OF PURIFYING MONOGLYCERIDES FORMED BY SUPERGLYCERINATED REFINED FATS TO SEPARATE THEREFROM MATERIALS TENDING TO CAUSE REVERSION OF FLAVOR AND ODOR, WHICH COMPRISES TREATING THE MONOGLYCERIDES WITH A SHORT CHAIN ALIPHATIC KETONE AS THE SOLVENT THEREFOR AT A TEMPERATURE AT WHICH A SINGLE PHASE IS FORMED, REDUCING THE TEMPERATURE TO CAUSE THE FORMATION OF TWO DISTINCT PHASES, ONE OF SAID PHASES CONTAINING MONOGLYCERIDES AND THE OTHER OF SAID PHASES CONTAINING THE REVERSION-CAUSING MATERIAL, AND RECOVERING THE MONOGLYCERIDES FROM THE FIRSTMENTIONED PHASE. 